Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$87.87	3.827%	$91.2328	$91.23	$91.25	$91.20
Purchase #2	$99.72	7.487%	$107.186	$107.19	$107.20	$107.20
Purchase #3	$29.39	9.219%	$32.0995	$32.10	$32.10	$32.10
Purchase #4	$99.79	4.253%	$104.0341	$104.03	$104.05	$104.00
Purchase #5	$77.66	10.365%	$85.7095	$85.71	$85.70	$85.70
Purchase #6	$110.77	6.324%	$117.7751	$117.78	$117.80	$117.80
Purchase #7	$113.35	12.830%	$127.8928	$127.89	$127.90	$127.90
7 purchase totals =	$618.55		$665.9298	$665.93	$666.00	$665.90